The present invention relates to opto-electric sensors suitable for measurements in environments in which strict safety requirements exist. In particular, the present invention is suitable for use in fluid level measurements of liquid fuel or temperature measurements. The present invention combines the advantages of high frequency electrical transducers with the advantages of optoelectronic interfacing.
Given strict requirements for electrical insulation or safety, indirect methods of measurement are preferred. For instance, according to the safety guidelines of the International Electrochemical Commission, when taking measurements in a Zone O hazardous environment, such as where explosive gas-air mixtures exist, no electrical equipment should be used, except for specifically certified circuits that are intrinsically safe.
In the past, the following measurement techniques have been utilized: floating mechanical displacement, hydrostatic, ultrasonic, x-ray and fiber optic methods for continuous liquid level measurement; and radiation sensors and fiber optic sensors for temperature measurements.
A disadvantage of the prior art methods has been that the sensors utilized typically have been quite complicated and expensive. Another disadvantage is that the accuracy of these methods is lower than the accuracy of some purely electrical methods. Unfortunately, these electrical methods typically don't meet the strict safety requirements as discussed above. For example, high frequency capacitive transducers are, in principle, quite accurate, but such prior art transducers typically have direct electrical connections to the gauging or monitoring systems and direct electrical connections to an external battery or to a sensor resident watch type battery, either of which negates use of the sensor in hazardous environments.